The use of radiation in wavelength-selective, non-ablative laser treatment of dermatological defects is gaining acceptance in the medical community. The term non-ablative here means that the delivery of laser radiation to an area of tissue being treated does not directly cause tissue removal or cause an open wound which must subsequently heal. By way of example, such non-ablative treatments are used, are at least being investigated, for wrinkle (rhytid) reduction, reduction of acne scars, and treatment of vascular disorders such as port-wine stains. Wavelengths most often used in these treatments are in the visible region or the near infrared region of the electromagnetic spectrum.
In these treatments, the area of tissue to be treated is often greater than an area that can be instantly illuminated by a treatment beam. This requires that a treatment beam be moved over the area to be treated until the entire area has received a prescribed dosage of laser radiation. It is important in moving a laser beam over an area to be treated that there are no untreated portions or voids within the treated area. Attempting to avoid such untreated areas by overlapping individual areas corresponding to the instantaneous beam size, however, can lead to a possibility that dosage in overlapped areas can be sufficiently high to cause at least patient discomfort and possibly even wound formation.
One method that may be used to move a beam over an area of tissue to be treated in a controllable manner is to deliver the beam via a hand-holdable scanner (scanning handpiece) which rapidly scans a pulsed beam in a preprogrammed pattern of irradiation spots. One such scanning handpiece is described in U.S. Pat. No. 5,743,902, granted to Trost incorporated herein by reference. This handpiece includes a pair of galvanometer mirrors for performing the programmed scanning. Radiation to be scanned is delivered by an articulated arm to the handpiece. The mirrors in the handpiece direct the radiation to the tissue via a lens for focusing the radiation on the tissue. The mirrors are located at about an effective focal length (EFL) of the lens from the lens, in a telecentric arrangement. This provides that the beam size at the tissue remains about the same with variations in the position of the handpiece from the tissue.
A disadvantage of the Trost handpiece is that it projects an essentially circular beam. This means that individual beam areas must be overlapped to avoid leaving voids in the treatment area. There is also no provision in the handpiece for controlling intensity of radiation over the area of a projected beam. The Trost handpiece is intended primarily for use in ablative applications using mid to long-wavelength infrared radiation. Such applications include skin resurfacing and making surgical incisions. In these applications the overlapping and lack of intensity distribution control present no particular problems.
A scanning handpiece for non-ablative treatments, however, ideally, should project a beam in which the radiation intensity distribution across the beam is as near uniform as possible. Preferably also, the uniform-intensity beam should have a cross-sectional shape such as a square, a rectangle, or a regular hexagon. This would allow an area greater than the beam area to be covered by side-by-side placements (tiling) of beam areas without leaving voids and, if desired, without overlapping. Further, such a scanning handpiece should be configured to receive radiation delivered thereto by an optical fiber. Optical-fiber delivery is a preferred method for delivering visible and near infrared radiation from lasers generating the radiation to a treatment site or a handpiece.